Peavey 6505 bias instructions

Written by dave n.
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Peavey 6505 bias instructions
Switching resistors allows the 6505 to bias hotter or colder, depending on user preference. (set of resistors image by evvigo from

When Eddie Van Halen's agreement with Peavey expired, so did the signature names such as "Wolfgang" and "5150." However, the designs and quality building methods did not expire. Peavey continued to build products that contained the various ingenious characteristics that were developed to Eddie Van Halen's expectations. The same is true of Peavey's amplifier line-up. The 6505 is exactly the same amplifier as the 5150 with the exception of the name and included bezel on the amplifier enclosure.

Skill level:

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Things you need

  • Philips screwdriver
  • Schematic of the Peavey 6505 amplifier
  • Wire clippers
  • 24AWG wire
  • 6.2k ohm 1/4W resistor
  • 10k ohm trimmer potentiometer
  • Soldering Iron (25W +)
  • Solder (60/40 Blend)

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  1. 1

    Remove the chassis from the enclosure of the 6505 with the screwdriver by loosening the screws mounting it in place.

  2. 2

    Examine the schematic and locate the 15k ohm resistor marked R68. Find the actual resistor on the circuit board, noting the 10uf 160V capacitor immediately next to it.

  3. 3

    Use the wire clippers to disconnect R68, making sure to trim as much of the leads back to the circuit board itself without damaging the board or surrounding components. Use the wire clippers to prepare a 2-inch piece of the 24AWG wire by stripping both ends of the wire approximately 1/8th inch.

  4. 4

    Mechanically connect the 6.2k ohm resistor to a lead of the trimmer potentiometer other than the wiper lead. Mechanically connect the wiper lead and remaining outer lead together. Solder the mechanical connections using the soldering iron and solder. Solder the prepared wire to the wiper lead connection as well.

  5. 5

    Turn the trimmer potentiometer fully clockwise. Mechanically connect the available lead of the 6.2k ohm resistor to one of the exposed leads of the 10uf 160V capacitor that was immediately next to R68. Mechanically connect the available lead of the 24AWG wire to the other exposed lead of the 10uf 160V capacitor.

  6. 6

    Solder the mechanical connections of the trimmer assembly to the 10uf 160V capacitor using the soldering iron and solder. The 6505 is now biased to its coldest setting and can be adjusted to a desired level turning the trimmer pot counter clockwise to bias the amplifier "hotter."

Tips and warnings

  • Be sure not to apply the tip of the soldering iron to the capacitor leads for more than two seconds at a time. Applying too much heat can desolder the capacitor from the circuit board making the amplifier malfunction. Use a hot glue gun to secure the trim pot assembly to the void area where the original safety resistor was installed.
  • Guitar amplifiers can carry lethal levels of voltage, particularly when it comes to tube amplifiers, even when they are turned off and unplugged from the wall, which can cause personal injury and even death from electric shock. If unsure of capabilities, consult a professional technician.

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